The present invention relates to cable ties.
Cable ties, also known as harnessing devices, are well known in the art and are commonly used to bundle a plurality of objects, such as cables. Cable ties typically comprise an elongated strip of material, such as plastic, having a head at one end, a tail at the other end and either teeth or rungs disposed along the length of the tail. Typically, the head of such cable ties comprise a strap accepting channel and a locking pawl which extends into the strap accepting channel, the locking pawl being pivotally disposed within the head of the cable tie about a thin, flexible hinge.
In use, cable ties typically function in the following manner to bundle a plurality of objects. Insertion of the tail of the tie into the strap accepting channel causes the locking pawl to pivot, thereby enabling the tail to be further advanced through the head until the cable tie takes the shape of a loop around the bundle of objects. Upon release of the insertion force, the pawl of the cable tie pivots back to its original position about the flexible hinge and lockably engages the tail in position around the bundle, the tail being incapable of removal once it is inserted in the head.
As an example of one type of cable tie, in U.S. Pat. No. 5,642,554 to S. C. Sorensen et al, there is disclosed a cable tie having an enhanced locking engagement between a pawl and ratchet teeth on a tongue. The cable tie includes an elongated tongue and a locking head having a movable pawl that is hinged at one side of an opening in the locking head across the opening from an abutment surface for locking engagement with a first set of ratchet teeth on one broad side of the tongue when the tip of the tongue has been inserted through the opening and teeth on the abutment surface for locking engagement with a second set of ratchet teeth on the other broad side of the tongue when the tip of the tongue has been inserted through the opening, and in which the side of the pawl including the pawl teeth converges toward the opposite side of the pawl in the direction of insertion, locking engagement is enhanced by the locking surface of at least one pawl tooth extending toward the apex of such tooth at an angle inclined toward the direction of insertion for locking engagement with a tooth of the first set of ratchet teeth; and by the locking surface of at least one of the first set of ratchet teeth extending toward the apex of such tooth at an angle inclined away from the direction of insertion for locking engagement with a pawl tooth.
As another example of another type of cable tie, in U.S. Pat. No. 4,688,302 to J. E. Caveney et al, there is disclosed an integral one-piece cable tie including an elongated flexible strap having a row of teeth thereon, a frame integral with one end of the strap and having an abutment wall and an entry surface and an exit surface and a strap-receiving opening extending therethrough, a pawl pivotally mounted by a hinge within the opening and having a set of teeth thereon shaped complementary to the row of teeth, wedging surfaces on the facing portions of the frame and the pawl, the thickness of the hinge being less than the thickness of the strap so as to accommodate sliding movement of the pawl toward the entry surface with the wedging surfaces in contact, thereby to move the set of teeth toward the abutment wall to grip the strap therebetween.
It should be noted that cable ties of the type described above often experience pawl failure. Specifically, in use, the lockable pawl engages at least one of the teeth or rungs on the strap of the cable tie and wedges the strap against an abutment surface which is across the strap accepting channel from the pawl. As a consequence of this particular design, it has been found that the entire load of the locking force of the pawl is displaced onto the relatively weak hinge of the pawl. As a result, the application of a significant withdrawal force tends to break the pawl hinge, thereby rendering the cable tie nonfunctional.
It should also be noted that pawl failure can not be remedied by strengthening the pawl hinge of the cable tie because the pawl hinge must be weak and flexible enough to permit the pawl to pivot during use.